Problem: $ { \left[\begin{array}{rrr}{1} & {0} & {-2} \\ {-1} & {-1} & {1}\end{array}\right]+\left[\begin{array}{rrr}{3} & {-2} & {1} \\ {1} & {2} & {-2}\end{array}\right] = {?} } $
To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{1}+{3} & {0}+{-2} & {-2}+{1} \\ {-1}+{1} & {-1}+{2} & {1}+{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{4} & {-2} & {-1} \\ {0} & {1} & {-1}\end{array}\right]}$